Preparation of cinnamaldehyde



l atented Nov. 7, 195

PREPARATION OF CINNAMALDEHYDE Henry H. Richmond, Guelph, Ontario, Canada, assignor to United States Rubber Company, New York, N. Y., a corporation of New Jersey No Drawing. Application April 5, 1947,

Serial No. 739,661

3 Claims.

' This invention relates to the preparation of cinnamaldehyde by the alkaline catalyzed condensation of acetaldehyde and benzaldehyde according to the equation Y p H 0110- CH=CHCO 1120 I omcno It has been found that a high yield (i. e., on the order of 75-85%, based on the benzaldehyde) of cinnamaldehyde can-be obtained by adding the acetaldehyde gradually to the benzaldehyde. A reversal in the order of addition, or the simultaneous mixing, of the reagents results in low yields, i. e., on the order of 18, and 49%, respectively.

Preferably, the reaction is carried out at a moderately elevated temperature such as '70. C., although this reaction temperature may be varied from 60-80 C. without too substantial a loss in yield. As usual in this condensation a dilute alkalicatalyst is used, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, trimethyl benzylammonium hydroxide, etc. The addition of the acetaldehyde to the benzaldehyde avoids'having present at'any time an excess of acetaldehyde and thereby minimizes the self-condensation of the acetaldehyde as well as the further condensation of cinnamaldehyde with acetaldehyde. By condensing a molecular'proportion of the acetaldehyde with a slight excess over a molecular proportion of the benzaldehyde, there 'is maintained throughout, an excess of benzaldehyde which tends to prevent to some extent the .iorniation of high boiling products which may be formed in part if the acetaldehyde were in excess to condense with formed cinnamaldehyde as aforesaid.

The acetaldehyde used in this process may be added as a liquid or a gas or in aqueous solution. Further, it is not necessary that the benzaldehyde be highly purified. Technical grades of benzaldehyde containing small amounts of chlorine may be used, since the chlorine containing impurities are removed in the final fractionation of the cinnamaldehyde. The quality of the cinnamic aldehyde obtained is very good, analyzing as high as 99 pure and is suitable for the preparation of flavors and perfumes.

The pH of the reaction mixture should be maintained by the addition of alkali from time to time in the region of 8 to 12, and especially from'BB to 10. This isconveniently done by staying in the pink range of phenolphthalein indicator. The pH of the reaction mixture tends to fall due to the formation of benzoic acidfrom the benzaldehyde. .At the enclof the reaction the mixture is slightly acidified to remove the alkali and then is made slightly basic by the addition of sodium bicarbonate., In practice it has been found easier to. acidify and then make faintly alkaline with sodium bicarbonate, than to reach the same pH by addition of acid; this procedure removes anybenzoic acid present.

The unreacted benzaldehyde can be recovered by fractional distillation and in the same fractionation, cinnamaldehyde is obtained in a state of -high purity leaving behind high boiling by-products.

The duration of theperiod of time in which the acetaldehyde is added to the reaction mixture materially affects theyield of cinnamaldehyde obtained. For the batch size and efiicient stirring, as set forth in Example 1, the preferred addition time is 90 minutes, although this addition time may be varied from 1 hour to 2 hours without too substantial a loss in yield. When the addition time is lowered from 90 minutes to 20 minutes the yield falls from 81% to 72%. When the addition time is increased from 90 minutes to 3 hours the yield falls from 81% to 68%. I

The duration of the period of time subsequent to the addition of the acetaldehyde, and during which the reaction mixture is stirred while maintaining the temperature at 70 C., materially af fects the yield of the cinnamaldehyde obtained. For the batch size and efiicient stirring described in Example 1, the preferred'duration of the 'period of time subsequent to 'the addition. of .the 'acetaldehyde and during which the reaction mix ture is stirred While maintaining the temperature at C., is minutes, although this period of time may be varied from 30 minutes to 3 hours without too substantial a loss in yield.

When this period of time is increased to 4' hours the yield falls from 81% to 70%.

The ratio of the total Weight of the aqueous alkali medium to the weight of benzaldehyde and acetaldehyde that are condensed, affects the yield obtained and the reaction time, since this factor in addition to the concentration of the alkali in the aqueous medium regulates the ratio of benzaldehyde and acetaldehyde to the hydroxyl ion present which acts as catalyst. The preferred ratio of the weight of aqueous alkali medium to the Weightof benzaldehyde and acetaldehyde is 5:1, althou h the ratio may be varied of water.

from 6.5:1 to 2.511 without too substantial a loss in yield. Decreasing the reaction volume increases the productivity of the equipment used.

The high boiling by-product which is recovered after the removal of the unreacted benzaldehyde and the cinnamaldehyde is a pleasant smelling oil'which issuitable as a masking odorant for such industrial products as rubber.

The following example is given to illustrate the invention.

Example To a 2000 cc. three-necked flask equipped with a thermometer, a reflux condenser, a stirrer, and a calibrated addition burette, jacketed so that it can be cooled by tap water, and whose tip is inserted below the surface of the reaction mixture, there is introduced 150 g. of technical benzaldehyde and a solution of 3.0 g. of sodium hydroxide in from 500 to 1300, preferably about 1000 cc. 7 The temperature of the mixture is TO-'0; is about the optimum temperaturefor high yields concurrent with the other conditions described in this example but the carried out in the range 60=80 C. Maintaining this temperature, 48 gramsof acetaldehyde is introduced through the addition burette, uniformly over a p'eriodof 1 hours. This constitutes the period for one-half of the reaction. The alkalind ity of the reaction mixture-is periodically checked and adjusted so that it is pink to phenolphthalein indicator by the addition of small quantities of sodiumhydroxide solution. 'Thi acidification is due-to the oxidation of benzaldehyde to benzoic acid. The optimum alkalinity is that indicated by thepink color of the phenolphthalein indicatorr The stirring is continued for another hour and a half at thesame temperature.

l he reaction'mixture is then acidified to pH 4 with aqueous sulfuric acid solution, and allowed to cool to room temperature; the excess sulfuri'c acid and anybenzoic acid present is neutralized with an excess of sodium bicarbonate bringing the pH to 8. The slightly alkaline mixture" is extracted with water insoluble organic solvent (200 cc. of benzene) and the whole is sub-'- sequently. poured into a sep'aratory funnel. The organic layer is separated; most of the solvent and all the water is removed by atmospheric flash distillation, and the residue consisting of; benzaldehyde, cinnamaldehyde, and high boilin byproducts, fractionated invacuo. v i ''..:The products are: 63.9 g. benzaldehyde boiling at 63? C. and15. mm. n =1.546; 86.9 g. cinnamal dehyde boiling at 123 C. and mm. n ;1.622,'

' and a: higher boiling residue of g. This representsa yield of 81 and a conversion of 46%. By

reaction can be raised, with stirring, to 70 C. The temperature analysis the cinnamaldehyde is found to be 90% pure.

While I have shown and described various embodiments of the invention, it is to be understood that the invention is susceptible to other modifications which appear Within the spirit of the invention and the scope of the appended claims.

Having thus described my invention, what I claim and desire to protect by Letters Patent is:

1. A method for preparing cinnamaldehyde which consists in heating a mixture of benzaldehyde and aqueous alkali solution of a concentration of from 0.23 to 0.6% by weight at a temperature of from to C. while gradually adding thereto acetaldehyde over a period of time of from one hour to two hours, the amount of benzaldehyde exceeding that molecularly equivalent to the total acetaldehyde employed, thereafter heating the resulting mixture at the same temperature for a period of time of from thirty minutes to three hours, agitating the mixture throughout said heating steps, maintaining the pH of the reaction mixture atfrom 8.011012 throughout. said heating steps, maintaining. molecular excessof v benzaldehyde over acetaldehyde in the reaction mixture throughout said heating steps, and r ecovering cinnamaldehyde from, the resulting reaction mixture. v

2. The method (if claim 1 wherein said cinnamaldehyde is recovered from the reaction mixture and from any benzoic acid present therein by acidifying the reaction mixture, neutralizing the d fied mixtur Wi er; ex ess sesii b carbonate an her rneut i n y e zoi acid present, and separately recovering cinnamaldehyde and the unreacted benzaldehyd i m the resulting mixture by a method incIuding f-rac} tional distillation.

"3. The proc sef cla ml whe ei a h o a d Periqdsof time. is subst ntially mine eawhere in the weight ratio of aqueous alkali medium to benzaldehyde plus ace alde yd is subs ntially 1.1 and wher insa d. e p ratur sub a tially 7.0? C. V

REFERENCES cumin. 7 The following references are of record the file or this patent? I i UNITED STAT-Es P T .Nllmber 7 Date-r 531,053 Apr; 20km! 1,715,822 Kno t. 1 42 I I FQBEIG JPATEN Numbi'i eo r'r Date.

mel e V 

1. A METHOD FOR PREPARING CINNAMALDEHYDE WHICH CONSISTS IN HEATING A MIXTURE OF BENZALDEHYDE AND AQUEOUS ALKALI SOLUTION OF A CONCENTRATION OF FROM 0.23 TO 0.6% BY WEIGHT AT A TEMPERATURE OF FROM 60 TO 80* C. WHILE GRADULLY ADDING THERETO ACETALDEHYDE OVER A PERIOD OF TIME OF THERETO ACETALDEHYDE OVER A PERIOD OF TIME OF FROM ONE HOUR TO TWO HOURS, THE AMOUNT OF BENZALDEHYDE EXCEEDING THAT MOLECULARLY EQUIVALENT TO THE TOTAL ACETALDEHYDE EMPLOYED, THEREAFTER HEATING THE RESULTING MIXTURE AT THE SAME TEMPERATURE FOR A PERIOD OF TIME OF FROM THIRTY MINUTES TO THREE HOURS, AGITATING THE MIXTURE THROUGHOUT SAID HEATING STEPS, MAINTAINING THE PH OF THE REACTION MIXTURE AT FROM 8.0 TO 12 THROUGHOUT SAID HEATING STEPS, MAINTAINING A MOLECULAR EXCESS OF BENZALDEHYDE OVER ACETALDEHYDE IN THE REACTION MIXTURE THROUGHOUT SAID HEATING STEPS, AND RECOVERING CINNAMALDEHYDE FROM THE RESULTING REACTION MIXTURE. 